Method for preparing graphene ribbons

ABSTRACT

Disclosed is a method for fabricating graphene ribbons, comprising: preparing a graphitic material comprising stacked graphene helices; and cutting the graphitic material in a short form by applying energy to the graphitic material; and simultaneously or afterward, decomposing the graphitic material into short graphene ribbons. This method provides a mass production route to graphene ribbons.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure relates to subject matter contained in priorityKorean Application No. 10-2000-0082512, filed on Aug. 22, 2008, which isherein expressly incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for preparing grapheneribbons, and particularly, to a method for fabrication of graphene inthe form of a ribbon.

2. Background of the Invention

Graphene, a single layer trigonal carbon honeycomb with a thickness ofabout 4 Å (refer to FIGS. 1(A) and 1(B)), has enormous potential due toits outstanding physical properties compared even to single-wall carbonnanotubes. It is the basic unit of C₆₀, multi-walled carbon nanotubes(MW CNTs), and graphite.

Due to the weak van der waals attraction between graphene layers, thetwo-dimensional material is obtainable when the forces between grapheneplanes are disrupted. Micromechanical cleavage is the most assuredmethod for fabricating graphene, but the yield is too small. The yieldof pure graphene in a chemical route, which has been proposed as a massproduction method, is also as low as around 0.5%. Graphene formed on ametal substrate by chemical vapour deposition (CVD) methods producemostly multiple graphene layers.

On the other hand, there have been efforts to prepare short carbonnanotubes by cutting multi-walled carbon nanotubes (known as anon-crystalline turbostratic structure, refer to FIG. 2) with amechanical method such as ball milling or a chemical method (refer to L.Chen et al., [Materials Letter 60 (2006) 241-244], N. Pierard et al.,[Chemical Physics Letters 335 (2001) 1-8], Z. Konya et al., [Carbon 42(2004) 2001-2008], and Z. Gu et al., [Nano Letter 2 (2002) 1009]).However, graphene could not be obtained by such efforts.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a massproduction route to graphene ribbons, thus opening up industrialapplications utilising the large scale i.e., tonnes a year, of thisinnovative carbon.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described herein,there is provided a method for preparing graphene ribbons, crumbling thegraphitic materials composed of long graphene helices (˜μm in length)(refer to FIG. 3) into short graphene ribbons (˜50 nm in length) byapplying energy (refer to FIGS. 4(A)-(D)). The graphene ribbon basedmaterials are stacked of AA′ (refer to FIGS. 3 and 5) or turbostratic(refer to FIG. 2) of which an interlayer bond force is weaker than thatof an AB (refer to FIGS. 1(A) and 1(B)). This development provides amass production route to graphene ribbons, thus opening up industrialapplications utilising the large scale i.e., tonnes a year, of thisinnovative carbon.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1(A) is a schematic diagram of graphite with an AB stackedstructure, and FIG. 1(B) is a planar view of AB graphite showing thefeature of the AB stacking of graphene layers;

FIG. 2 is a planar view of turbostratic graphite showing the feature ofthe disordered turbostratic stacking of graphene layers;

FIG. 3 is a schematic diagram showing a tubular graphitic materialcomprising AA′ stacked graphene helices;

FIGS. 4(A)-(D) are schematic diagrams showing processes for preparinggraphene ribbons according to an embodiment of the present invention;

FIG. 5 is a planar view of AA′ graphite showing the feature of the AA′stacking of graphene layers;

FIG. 6(A) is a planar view showing the crystal structure of AA′graphite, and FIG. 6(B) is a schematic diagram showing a space group ofthe AA′ crystal;

FIG. 7 is a planar view of AA graphite showing the feature of the AAstacking of graphene layers;

FIG. 8 is XRD patterns for samples with milling. Characteristic (002),(100), (004), (011) and (200) peaks for AA′ graphite were graduallybroadened with milling. The arrowed peaks could be assigned to metalimpurities originated from the steel balls; and

FIGS. 9(A)-(C) shows transmission electron microscope (TEM) images forpristine materials (A) and the samples milled for 1 hour (B) and 2 hours(C). The tubular AA′ stacked graphitic material (A) was totallydestroyed by a two hour (Spex) milling (C), through to the graphiticribbons where thickness is ˜5 nm (B).

DETAILED DESCRIPTION OF THE INVENTION

Description will now be given in detail of the present invention, withreference to the accompanying drawings.

A method for preparing graphene ribbons according to the presentinvention comprises (1) preparing graphite composed of helically stackedgraphene ribbons, (2) cutting the graphitic material into a short formby applying energy to the graphitic material and (3) simultaneously withor followed by, decomposing an interlayer bond force thereby splittingthe graphitic material into short graphene ribbon.

Hereinafter, the respective steps will be explained in more detail withreference to the attached drawings.

Preparation of the Graphitic Material

Graphitic material 1 according to the present invention has a structurethat graphene ribbons 2 have helically grown along a long axis (refer toFIG. 3 and FIG. 4(A)). Here, the graphitic material 1 has a structurethat at least two long-ribbons stacked.

Referring to FIG. 3, the graphitic material 1 is composed of helicallygrown long-ribbon shaped graphene formed by dislocation 3. The graphiticmaterial 1 has a high aspect ratio more than 10, a diameter of several˜several hundreds of nm (e.g., 2˜300 nm) and a length of several μm. Thegraphene ribbons 2 constituting the graphitic material have a widthof—several tens of nm (generally, less than about ¼ of the diameters ofthe raw material, or ½ of the diameters of the graphitic material whenit does not have a complete tubular shape), and have a lengthcorresponding to that of the graphitic material.

The graphitic material may have a tubular or a fibrous shape. However,the present invention is not limited to those shapes, but can beimplemented only that the graphene ribbon stacked body helically growsalong the long axis.

The stacking type of graphene ribbons in the graphitic material may havea turbostratic (refer to FIG. 2) or an AA′. The turbostratic structureindicates the disordered stacking of graphene (i.e., there is noregularity in stacking between graphene layers). And, as shown in FIGS.3 and 5, the AA′ stacked structure is a structure that alternategraphene layers exhibiting the AA′ stacking are translated by a halfhexagon (1.23 Å).

The AA′ stacked structure is comparable with AB stacked structure (ABstacked graphite) known as the only crystalline graphite, and an AAstacked structure (AA stacked graphite) that can not energetically existin nature but can be formed by intercalation of Li between graphenelayers.

AB stacked graphite is described by a space group of a hexagonal (#194).Here, a=b=2.46 Å, c=6.70 Å, α=β=90° and γ=120°. That is, an interplanarspacing of the AB graphite is 3.35 Å A i.e., ½ of c.

AA stacked graphite is described by a space group of a simple hexagonal(#191). Here, a=b=2.46 Å, c=3.55 Å, α=β=90° and γ=120° (refer to FIG.2). That is, an interplanar spacing of AA stacked graphite is 3.55 Å.

The structure of AA′ stacked graphite of the present invention could notbe described with all of the 230 crystal space groups. Thus, we assignedthe crystal structure of AA′ graphite to a simple hexagonal space group.Four atoms, consisting of two atoms on each of the A and A′ layers, arecontained within the primitive unit cell of AA′ graphite. The former twoatoms at (⅓, ⅔, ½), (⅔, ⅓, ½) are linked to the 2(d) site (⅓, ⅔, ½) ofthe space group whereas the latter two atoms at (⅙, ⅚, 0), (⅚, ⅙, 0)cannot be defined in the space group. Two kinds of both the (100) andthe (110) planes appear, and we designate the distinctive planes as(100)* and (100)*, respectively. Due to a lack of experimental dataconcerning the atomic positions within the space group the X-raydiffraction (XRD) pattern of AA′ graphite was derived from that of AAgraphite and it can be also derived from other space groups,particularly orthorhombic or monoclinic space group. The (001), (100),(102), (002), (014), (110), (112), (006), (200) and (022) peaks appearin the pattern of AA graphite. The (h01), (0k1) and (hk1) reflectionsare absent in AA′ graphite, due to the insertion of additional atomsfrom the A′ graphene layers into the eclipsed AA form. As a result theavailable reflections for AA′ graphite are due to the (002), (100),(004), (110), (006) and (200) planes, where the intensity of the (110)plane, that is (110)*, should be stronger due to the periodic overlap ofgraphene layers, as shown in FIG. 6A ((006) (2θ=84.4°) and (200)(2θ=92.6°) peaks are normally not observed because their intensities aretoo weak). One outstanding feature of the pattern of AA′ graphite is thedisappearance of the (101) peak (2θ=44.6°), the (102) peak (2θ=50.4°)and the (112) peak (2θ=83.4°); the intensities are relatively strongwithin the pattern of AB graphite. Thus, the absence of the (101), (102)and (112) peaks within the XRD patterns of graphitic materials is acriterion for AA′ graphite.

The graphitic material comprising graphene ribbons of the presentinvention is generally obtainable with CVD (chemical vapour deposition)processes, using hydrocarbon gases such as C₂H₂, C₂H₄, CH₄ as a sourceof carbon under a vacuum state (below 760 Torr). Deposition temperaturesare normally lower than 1000° C. Particularly, plasma assisted CVDprocesses can synthesize the graphitic material even at a lowtemperature of 500˜700° C.

Preparation of Graphene Ribbons

The graphitic material comprising graphene ribbons prepared in the firststage is decomposed into short graphene ribbons by applying energy tothe graphitic material (refer to FIGS. 4(A)-(D)). For instance,mechanical cutting of the graphitic material having a large aspect ratiointo a length less than a predetermined length (about several hundredsnm) can decompose it into short graphene ribbons 2 because the bindingenergy between graphene layers (Van der Waals bond) is weak. This is thesame principle that straw bundles are decomposed into straws when thestraw bundles are cut into a short length.

Methods for cutting the graphitic material may include a mechanicalmethod (ball milling), a chemical method, and an electrical method(ionic milling utilizing plasma). As the mechanical method of thepresent invention, may be used a two-roller milling method, a ballmilling method, an ultra high pressure spraying method, etc.

Mechanical ball milling is an easy method for fabricating grapheneribbons from a tubular graphitic material comprising AA′ stackedgraphene ribbons (similar to conventional multi-walled carbon nanotubes(MW CNTS)). Milling time to decompose the material into graphene ribbonsdepends on milling energy. For example, a spex milling apparatus, whichis known as efficient milling equipment, may completely decompose thegraphitic material into short graphene ribbons within several hours.However, the graphitic material may not be decomposed by a longermilling even up to 100 hours if we use a milling apparatus with a smallmilling energy.

In the case of using tubular graphite as the pristine material, aprocess for crumbling the graphitic tube inducing a stress (stresscrumbling) can be further included. The stress crumbling process isperformed by penetrating water into the tubular graphitic material andfreezing the water containing material. While the water is frozen, atensile stress occurs in the tube due to a volume expansion. And, thetensile stress destroys the material into graphene ribbons (or powder).Here, an additional treatment for the tubular material to alter itshydrophobic characteristic to hydrophilic characteristic can berequired.

Preferably, a sonication process after the crumbling processes (by theball milling or the stress crumbling) can be added to completely scatterthe crumbled graphene ribbons in liquid phase (refer to FIG. 4(C)).

Preferred Embodiment 1

Graphene ribbons were prepared by using a graphitic nanomaterial thatgraphene helices are stacked in an AA′ manner (similar to MW CNTs).Here, the graphite nano material has an average outer diameter of 20 nm(outer diameter distribution: 2˜50 nm), an average inner diameter of 3˜5nm (inner diameter distribution: 1˜10 nm), and a length of 2˜3 μm. Thesample was passed through a two-roller mill 50 times. This shortened itinto short material ˜200 nm in length. Then, the processed sample wasmade to undergo a hydrophilic treatment, and then was immersed intowater to penetrate water into the tube. Then, the short and watercontaining tubules were maintained at a temperature ˜10° C. for onehour, and then were melted. After a sonication (in alcohol) for 10minutes, obtained were graphene ribbons having a width of about ˜5 nmand a length of about ˜200 nm (thickness of about 4 Å).

Preferred Embodiment 2

The same tube-type of graphitic nano material as that of the preferredembodiment 1 was passed through a two-roller mill 100 times, therebyhaving a length decreased into about 100 nm or less. Then, the samplewas made to undergo a sonication process to be dried, obtained weregraphene ribbons having a width of about ˜5 nm and a length of about˜100 nm.

Preferred Embodiment 3

The same graphite nano material as that of the preferred embodiment 1was milled for two hours using a spex ball milling apparatus. As anobservation result for the milled sample by using a scanning electronmicroscopy (SEM), tubular materials were not observed. And, as an X-rayanalysis result, the characteristic peaks of (002), (100), (004), and(110) of the AA′ stacked crystal gradually disappeared as the millingtime increased (refer to FIG. 8). This means that the tube-type of AA′graphene stacked body has been decomposed into graphene ribbons (C)through to stacked graphene ribbons (B) with the milling time as shownin FIGS. 9(A)-(C). For one hour milling graphitic ribbons coexist withbi- or single-layer graphene (B). With a further one hour milling, thegraphitic ribbons were converted to graphene nanoribbons which areapproximately 10 nanometres in length (C). Stacked graphene fringes arepartially observed. Their average interplanar distance was measured tobe about 3.55 Å (C). This supports the analysis that the graphenenanoribbons are stacked in a disordered arrangement i.e., commonly namedturbostratic stacking.

Preferred Embodiment 4

Graphene ribbons were prepared by using carbon nano fiber composed ofhelical graphene (average diameter of 500 nm, and length of about 10μm). The sample underwent a milling process for two hours. As SEM andX-ray analysis results of the sample, the same results as those of thepreferred embodiment 2 were obtained. This shows that carbon nano fibercan be also decomposed into graphene by a milling process like themulti-walled carbon nanotubes.

Preferred Embodiment 5

The same tubular graphitic nanomaterial as that of the preferredembodiment 1 was prepared. To decompose the sample into graphene ribbonsby an electric (plasma) energy, it was irradiated by a 200 W argonplasma for 10 minutes. The plasma was generated in a pressure of 50mTorr. As an Atomic Force Microscopy (AFM) analysis revealed decomposedgraphene ribbons where a width and a length are 2-6 nm and 5-50 nm,respectively (thickness: 0.4-1 nm).

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present disclosure. The presentteachings can be readily applied to other types of apparatuses. Thisdescription is intended to be illustrative, and not to limit the scopeof the claims. Many alternatives, modifications, and variations will beapparent to those skilled in the art. The features, structures, methods,and other characteristics of the exemplary embodiments described hereinmay be combined in various ways to obtain additional and/or alternativeexemplary embodiments.

As the present features may be embodied in several forms withoutdeparting from the characteristics thereof, it should also be understoodthat the above-described embodiments are not limited by any of thedetails of the foregoing description, unless otherwise specified, butrather should be construed broadly within its scope as defined in theappended claims, and therefore all changes and modifications that fallwithin the metes and bounds of the claims, or equivalents of such metesand bounds are therefore intended to be embraced by the appended claims.

1. A method for preparing graphene ribbons, comprising: preparing agraphitic material where the graphitic material is composed of graphenehelices or helical graphene ribbons grown along its long axis; andshortening the graphitic material by applying an energy, simultaneouslywith or followed by, decomposing the graphitic material into grapheneribbons.
 2. The method of claim 1, wherein the graphene ribbon stackedmaterial is a turbostratic stacked structure or an AA′ stackedstructure, and wherein the AA′ stacked structure is a structure thatalternate graphene layers exhibiting the AA′ stacking are translated bya half hexagon (1.23 Å).
 3. The method of claim 1, wherein the graphiticmaterial has an aspect ratio more than 10, and has an outer diameter of2˜300 nm, and the graphene ribbons have a width equal to or less than ½of the outer diameter of the graphitic material.
 4. The method of claim1, wherein the graphene helices are formed by dislocation.
 5. The methodof claim 1, wherein the graphitic material is a tube shape or a fibrousshape.
 6. The method of claim 1, wherein the graphitic material isobtained by thermally-processing non-crystalline carbon material underan inactive atmosphere at a temperature of 1,000˜2,000° C., orperforming a chemical vapor deposition (CVD) method under conditionsthat hydrocarbon is used as reaction gas, an inner pressure of asynthesis container is 100˜1,000 Torr, a temperature of the synthesiscontainer is 600˜1,000° C., and a gas flow amount is 50˜200 sccm.
 7. Themethod of claim 1, wherein the graphitic material is a tube shape, andfurther comprising: performing a hydrophilic treatment to penetratewater into the tube, and cooling the water included tubular graphiticmaterial to induce a tensile stress.
 8. The method of claim 1, furthercomprising a sonication process to scatter the processed grapheneribbons.
 9. The method of claim 8, wherein the graphitic material isgraphite tube having a tube shape, and further comprising: performing ahydrophilic treatment for the cut graphite tube before the sonicationprocess, then penetrating water into the tube, and cooling the water,thereby unfolding the cut graphite tube by a tensile stress occurringdue to a volume expansion while the water freezes.